Synthesis and characteristics of interpenetrating polymer network hydrogel composed of chitosan and poly(acrylic acid)

Interpenetrating polymer network (IPN) hydrogels composed of chitosan and poly(acrylic acid) (PAAc) were synthesized by UV irradiation method, and their structure, crystallinity, swelling behavior, thermal property, and mechanical property were investigated. Chitosan/PAAc IPNs exhibited relatively high equilibrium water content and also showed reasonable sensitivity to pH. From the swelling behaviors at various pH's, Fourier transform infrared spectra at high temperature and thermal analysis confirmed the formation of polyelectrolyte complex due to the reaction between amino groups in chitosan and carboxyl groups in PAAc. For this reason, even at a swollen state, the present chitosan/PAAc IPNs possess good mechanical properties. Particularly, the CA‐2 sample (with a weight ratio of chitosan/PAAc = 50/50, molar ratio [NH₂]/[COOH] = 25/75) showed the lowest equilibrium water content and free water content, attributed to the more compact structure of the polyelectrolyte than CA‐1 or CA‐3 due to the high amount of interchain bond within the IPN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 113–120, 1999     

Characterization of anionic/cationic sequential IPNs. II. Studies of swelling,modulus, and alternate phase staining with CsF and LiI

Anionic/cationic interpenetrating polymer networks (IPNs) were synthesized by sequential polymerization from crosslinked polystyrene, PS, as polymer I and crosslinked poly(4-vinyl pyridine), P(4-VP), as polymer II. Ionomeric substitution of the two networks was based on sulfonation and quaternization of the phenyl and pyridine rings, respectively. The swelling, morphological, and dynamic mechanical behavior of ionomeric and unsubstituted IPNs was explored as a function of overall IPN composition. A theoretical analysis of the unsubstituted IPNs via the Thiele–Cohen equation showed that essentially no additional physical or chemical crosslinks were developed in the swollen state. Modulus studies showed that network I tends to dominate the mechanical properties in the bulk state. Swelling studies on the ionomeric IPNs as a function of pH demonstrated a complex change in behavior with the addition of NaCl, possibly due to an ionic screening effect. Electron microscopy involved alternate staining of the anionic and cationic phases using CsF and Lil and showed a two-phase structure, with the possibility of additional phases within phases due to separation of the ionomeric components. Comparison of the two staining techniques yielded strong evidence of a positive/negative–negative/positive phase contrast, depending on the phase being stained. In each case, domains were less than 100 nm (1000 Å), with the domain size decreasing as the P(4-VP) content increased. Also, a phase inversion appeared to occur between 50 and 80% P(4-VP). The dynamic mechanical studies supported the two-phase morphology and gave evidence of significant molecular mixing between the phases.     

Synthesis,characterization, and viscoelastic behavior of single-phase interpenetrating polystyrene networks

Single phase interpenetrating polystyrene networks were synthesized using a room temperature photopolymerization method. Divinylbenzene was used for crosslinking both networks in most cases; a few IPNs were prepared using acrylic acid anhydride to provide labile crosslinkages in the primary network. The IPNs were characterized by means of equilibrium swelling in toluene. The results of these experiments closely approached the predictions of a swelling equation derived under the assumption that the two networks were elastically independent. Deviations from the swelling equation predictions could be explained in terms of contributions from internetwork entanglements. Small amplitude dynamic mechanical measurements indicated that the presence of the small amount (～10 percent) of tight primary network chains had no perceptible effect on the linear viscoelastic properties.     

Biomimetic strain hardening in interpenetrating polymer network hydrogels

In this paper, we present the systematic development of mechanically enhanced interpenetrating polymer network (IPN) hydrogels with Young's moduli rivaling those of natural load-bearing tissues. The IPNs were formed by synthesis of a crosslinked poly(acrylic acid) (PAA) network within an end-linked poly(ethylene glycol) (PEG) macromonomer network. The strain-hardening behavior of these PEG/PAA IPNs was studied through uniaxial tensile testing and swelling measurements. The interaction between the independently crosslinked networks within the IPN was varied by (1) changing the molecular weight of the PEG macromonomer, (2) controlling the degree of PAA ionization by changing pH, and (3) increasing the polymer content in the PAA network. Young's moduli and the maximum stress-at-break of the swollen hydrogels were normalized on the basis of their polymer content. Strain hardening in the IPNs exhibited a strong dependence on the molecular weight of the first network macromonomer, the pH of the swelling buffer, as well as the polymer content of the second network. The results indicate that the mechanical enhancement of these IPNs is mediated by the strain-induced intensity of physical entanglements between the two networks. The strain can be applied either by mechanical deformation or by changing the pH to modulate the swelling of the PAA network. At pHs below the pK_a of PAA (4.7), entanglements between PEG and PAA are reinforced by interpolymer hydrogen bonds, yielding IPNs with high fracture strength. At pHs above 4.7, a “pre-stressed” IPN with dramatically enhanced modulus is formed due to ionization-induced swelling of the PAA network within a static PEG network. The modulus enhancement ranged from two-fold to over 10-fold depending on the synthesis conditions used. Variation of the network parameters and swelling conditions enabled “tuning” of the hydrogels' physical properties, yielding materials with water content between 58% and 90% water, tensile strength between 2.0 MPa and 12.0 MPa, and initial Young's modulus between 1.0 MPa and 19.0 MPa. Under physiologic pH and salt concentration, these materials attain “biomimetic” values for initial Young's modulus in addition to high tensile strength and water content. As such, they are promising new candidates for artificial replacement of natural tissues such as the cornea, cartilage, and other load-bearing structures.     

Silicone‐based hydrogels prepared by interpenetrating polymer network synthesis: Swelling properties and confinements effects on the formation kinetics

In this work, interpenetrating polymer networks (IPNs) of polydimethylsiloxane (PDMS) and poly(acrylic acid) or poly(2‐hydroxyethyl methacrylate) (PHEMA) have been synthesized employing a sequential method. Monomeric AAc or HEMA was introduced into the PDMS network by swelling the polymer in solutions of monomer. The polymerization of monomers was then conducted in the swollen network. The swelling properties of the IPNs were investigated by varying the monomer concentrations in the polymerization and more swelling was observed with low monomer concentrations due to the prevalence of cyclization reactions. Multi‐step polymerization used to achieve IPNs with high hydrogel contents, did not improve their water uptake. The kinetics of acrylic acid polymerization was studied under various conditions. Specifically, in the presence of confinement effects imposed by the PDMS network a considerable drop in the rate of reaction was observed. The cross‐linking density of the PDMS network was also studied how to affect the reaction rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical properties of interpenetrating polymer network hydrogels based on hybrid ionically and covalently crosslinked networks

Hydrogels are polymer networks swollen in water. Because of their soft and wet nature, and their ability to show large volume changes, hydrogels can be useful in many biomedical and actuator applications. In these applications, it is crucial to tune the mechanical and physical properties of a hydrogel in a controllable manner. Here, interpenetrating polymer networks (IPNs) made of a covalently crosslinked network and an ionically crosslinked network were produced to investigate the effective parameters that control the physical and mechanical properties of an IPN hydrogel. Covalently crosslinked polyacrylamide (PAAm) or poly(acrylic acid) (PAA) networks were produced in the presence of alginate (Alg) that was then ionically crosslinked to produce the IPN hydrogels. The effect of ionic crosslinking, degree of covalent crosslinking, AAm : Alg and AA : Alg ratio on the swelling ratio, tensile properties, indentation modulus, and fracture energy of IPN hydrogels was studied. A hollow cylindrical hydrogel with gradient mechanical properties along its length was developed based on the obtained results. The middle section of this hydrogel was designed as a pH triggered artificial muscle, while each end was formulated to be harder, tougher, and insensitive to pH so as to function as a tendon‐like material securing the gel muscle to its mechanical supports. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2504–2513, 2013     

药物缓释材料的合成与性能

研究了聚氨酯/聚醚半互穿网络聚合物的合成、溶胀行为和释放性能,特别是疏水组成、线型聚醚结构和温度对网络的溶胀平衡和溶胀动力学的影响。同时还测量了大分子肝素在填充时的分配系数和释放速度,并对肝素从溶胀的互穿网络聚合物中释放的机理进行了讨论。     

Studies on interpenetrating polymer networks based on nitrile rubber-poly(vinyl chloride) blends and poly(alkyl methacrylates)

Several interpenetrating polymer networks (IPNs) based on nitrile rubber-poly(vinyl chloride) blends and various alkyl methacrylates have been synthesized. The rubber blends were swollen in methacrylate monomers containing required amounts of initiator and crosslinker for specific time periods and then polymerized at higher temperature. The composition of the IPNs could be varied by changing the swelling time. The IPNs were characterized for their glass-transition temperature, dynamic mechanical properties, and tensile properties. The effect of structure and composition on the vibration damping characteristics of these IPNs are discussed. © 1994 John Wiley & Sons, Inc.     

Photomechanical effects in crosslinked photochromic polymers

The effect of radiation on photochromic crosslinked polymers containing azo group side chains is investigated. After irradiation at constant sample length, the swollen gels of light-sensitive polymers exhibit a reversible increase in the elastic retractive force. The light induced conformational changes are also accompanied by changes in the swelling equilibrium and temperature of the sample due to absorption of radiation and this added complication to the interpretation of the data. Interactions of the polymer with the solvent and the heat effect were eliminated by determining the temperature dependences of the elastic retractive force for the irradiated and unirradiated rubbery dry networks. The photomechanical effect increased with an increase in the content of photochromic groups and for the polymer with 5.4 mol % of azo groups, the photoinduced contraction of the sample amounted to 1%.     

Synthesis and characterization of pH‐ and temperature‐sensitive silk sericin/poly(N‐isopropylacrylamide) interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of silk sericin (SS) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared simultaneously. The properties of the resultant IPN hydrogels were characterized by differential scanning calorimetry and SEM as well as their swelling behavior at various temperatures and pH values. The single glass transition temperature (T_g) presented in the IPN thermograms indicated that SS and PNIPAAm form a miscible pair. The swollen morphology of the IPNs observed by SEM demonstrated that water channels (pores present in SEM micrographs) were distributed homogeneously through out the network membranes. The swelling ratio of the IPNs depended significantly on the composition, temperature and pH of the buffer solutions. The dynamic transport of water into the IPN membrane was analyzed based on the Fickian equation. Copyright © 2006 Society of Chemical Industry     

Effects of silicone rubber on properties of dielectric acrylate elastomer actuator

This article describes the effects of silicone rubber (SR) networks on the actuating behavior of acrylate rubber (AR)‐based dielectric actuators. SR chains were diffused into a swollen AR networks in the presence of a co‐solvent, and then the silicone chains were chemically crosslinked in an attempt to form an interpenetrating polymer network. The presence of SR in the AR network was confirmed by various instrumental analyses including attenuated total reflectance‐Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The total crosslink density based on a swelling method and tensile properties increased with modification time. The Maxwell stresses were also determined using a pure‐shear specimen. They increased in a parabolic fashion with the applied voltage, and depended on the type of compliant electrode and SR used. POLYM. ENG. SCI. 46:1455–1460, 2006. © 2006 Society of Plastics Engineers.     

Swelling of sodium chloride filled polybutadiene networks in water,water/ acetone and water/THF mixtures

The swelling of polybutadiene (PB) networks of different cross-link densities filled with finely divided sodium chloride (NaCI) particles are studied in water, water/acetone and water/THF mixtures. Swelling over periods of 2 months are recorded. The degree of swelling was observed to increase continuously in water during this period, whereas in water/acetone mixtures it reached a peak followed by deswelling and it converged to a maximal value in water/THF mixtures. The highly cross-linked samples exhibited unusually high degrees of swelling, and calculations indicated full stretching of the network chains. The enthalpic contribution to the chemical potential of the networks in equilibrium with solvent was determined using the phantom network model of rubber elasticity theory. The swollen network-salt system was approximated by the lattice model of polymer solutions. The positive contributions of water and acetone to the chemical activity of the swollen network were offset by the negative contribution of dissociation of salt in water, resulting in a small negative enthalpy of mixing. The highest rate of diffusion of solvent was observed for the PB/water/THF ternary system. Diffusion rates of pure water and water/acetone mixture were much smaller and of comparable magnitude. Mechanical measurements of stress and strain at break, and dynamic mechanical measurements of storage and loss moduli of filled and unfilled samples showed that filling with NaCl did not change the mechanical properties of the networks significantly, in spite of the dramatic change in the swelling behaviour.     

Entanglements in interpenetrating polymer networks evidenced by simple physicochemical investigations

A series of in situ sequential interpenetrating polymer networks (IPNs) of polyurethane (PU) and polystyrene (PS) were prepared at room temperature. The PU network was made from oligomeric polypropylene oxide, end-linked with an aliphatic triisocyanate. The PS network results from free radical photocopolymerization of styrene with a small amount of divinylbenzene. During synthesis, the homogeneous initial mixture segregates into co-continuous phases with no chemical bonds between them. However, the samples exhibit high optical transparency. The measurements of refractive index and equilibrium swelling in ethyl acetate gave the evidence of interpenetration, i.e. additional entanglements between unlike network chains.     

New Interpenetrating Polymer Networks of N-isopropylacrylamide/ N-acryloxysuccinimide: Synthesis and Characterization

Interpenetrating polymer networks (IPNs) based on poly (N-isopropylacrylamide), PNIPAAm, and poly (N-acryloxysuccinimide), PNAS, were prepared by a sequential method; the PNIPAAm which was polymerized and crosslinked by gamma irradiation, was swelled in a solution of PNAS/polylysine, which function as crosslinking agent for this monomer and as anchoring element of vesicles. The thermosensitivity properties (limit swelling time, lower critical solution temperature (LCST) and water retention), chemical composition (FTIR and elemental analysis), thermal properties (DSC and TGA) and morphology (SEM) were studied to characterize the IPNs.     

Polymer–protein interaction,water retention,and biocompatibility of a stimuli‐sensitive superporous hydrogel containing interpenetrating polymer networks

The swelling of a superporous hydrogel containing poly(acrylic acid‐co‐acrylamide)/O‐carboxymethyl chitosan interpenetrating polymer networks (SPH‐IPN) was sensitive toward the pH, ionic strength, and temperature stimuli. With insulin as a model drug, polymer–protein interaction was detected, and it was physical rather than covalent. Freezing water was the majority of the imbibed water in the swollen SPH‐IPNs, and the water‐retention ability of the polymer against compression and time of exposure at 37°C was improved as the amount of the O‐carboxymethyl chitosan network increased. A 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay on AD293 and RBL‐2H3 cells and an in situ lactate dehydrogenase assay and morphological study on rat intestine confirmed that the SPH‐IPNs had satisfactory biocompatibility. These pronounced properties suggested that the SPH‐IPNs could be developed as an attractive peroral delivery vehicle for peptide and protein drugs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Elastic and swelling behavior of 2-hydroxyethyl methacrylate,diethylene glycol methacrylate,and methacrylic acid copolymers

The elastic and swelling behavior of copolymers of 2-hydroxyethyl methacrylate, diethylene glycol methacrylate, and methacrylic acid crosslinked with ethylene glycol dimethacrylate has been studied. In the range of copolymer composition studied, Young's modulus of the swollen networks increases with the content of methacrylic acid, and its dependence on the content of diethylene glycol methacrylate passes through a maximum. The concentrations of the elastic network chains and determined from Young's moduli of swollen networks are much higher than those calculated from stoichiometry. This effect is attributed to the presence of additional physical crosslinks due to water-induced ordering of the hydrophobic backbone chains. Both the elastic and swelling behavior of the polymers mentioned above are decisive for their application in the preparation of soft contact lenses. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2141–2148, 1997     

Confinement effects on the kinetics of formation of sequential semi-interpenetrating polymer networks

Summary Peculiarities of formation kinetics of sequential semi-interpenetrating polymer networks based on crosslinked polyurethane with different cross-linking density and linear polystyrene and polybutylmethacrylate have been studied. Polyurethane networks were synthesized differing in molecular mass M_c of the chains between cross-links. Monomeric styrene and butyl methacrylate were introduced into these networks by swelling them in monomers up to equilibrium. The kinetics of polymerization of monomers in swollen networks was investigated. The experimental data show the dependence of the kinetic parameters of polymerization on M_c, this dependence being different for various monomers. Sharp discrepancy in molecular mass distribution of polymers formed in various matrices has been observed. The differences in dependencies of reaction kinetics and molecular mass distribution are supposed to be connected to various dependence of the chain growth and termination of various monomers on the density of network, i.e. on the confinements imposed by the intranetwork space.     

Gradient interpenetrating polymer networks. I. Poly(ether urethane) and polyacrylamide IPN

The swelling properties of poly(ether urethane)s and the preparation of interpenetrating polymer networks (IPNs) from a poly(ether urethane) thermoplastic elastomer and hydrogel forming polyacrylamide have been studied. The acrylamide monomer was polymerized with simultaneous crosslink formation, in the presence of the swollen thermoplastic elastomer. Upon removal of the swelling solvent, an IPN was obtained which absorbed water in the manner of a hydrogel but had mechanical properties superior to a hydrogel.     

Properties of electroresponsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

Interpenetrating polymer networks (IPNs) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) exhibited electrical-sensitive behavior. PAAc as an initial network was prepared inside a PVA solution using UV irradiation; then, PVA networks as a secondary network were formed by a repetitive freeze–thawing process. Their mechanical properties were influenced by the swelling ratio, crosslinking by UV radiation and a freeze–thawing process, and intermolecular force by hydrogen bonding. When a swollen PVA/PAAc IPN was placed between a pair of electrodes, the IPN exhibited bending behavior upon the applied electric field. The equilibrium bending angle (EBA) and the bending speed of the PVA/PAAc IPN increased with the applied voltage and the content of the PAAc network having negatively charged ionic groups within the IPN. The electroresponsive behavior of the present IPN was also affected by the electrolyte concentration of the external solution. Particularly, IPN37 showed a maximum EBA when the critical ionic strength was 0.1. Anisotropic deswelling of the IPN was observed in a direct contact with a pair of electrodes under aerobic conditions. The PVA/PAAc IPN also showed stepwise bending behavior depending on the electric stimulus. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1675–1683, 1999     

Effect of gamma irradiation on the interpenetrating networks of gelatin and polyacrylonitrile: Aspect of crosslinking using microhardness and crosslink density measurements

The present article reports the effect of gamma irradiation on the hardness behavior of the interpenetrating polymer networks (IPNs) of gelatin and polyacrylonitrile (PAN). Various compositions of gluteraldehyde‐crosslinked gelatin and N, N′‐methylene bis acrylamide (MBA)‐crosslinked PAN were prepared and investigated for microhardness studies. The pre‐ and post‐irradiated IPNs were characterized for their crosslinking density, determined with swelling ratio measurements. It was found that the crosslinked IPNs get further hardened because of radiational hardening at specific doses in the range from 2 to 250 kGy. The role of acrylonitrile and crosslinker (MBA) in the IPNs, as a consequence of irradiation, has also been explained. A fair consistency has been observed between the microhardness results and crosslinking density measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2581–2586, 2006